There is growing recognition that fundamental issues in basic research in the health sciences must develop increasingly powerful theoretical approaches for both understanding and controlling complex systems at multiple levels of organization. The proposed research addresses this problem by extending, theoretically, methodologically, and conceptually, the use on individual-based modeling to the study of individual, social and group behavior. The proposed research is unique in that one of its central aims is to evolve models (e.g., using simulated annealing or genetic algorithms) from data, resulting in surrogate individuals that behave like the complex organisms studied. The goals of the proposed research will be achieved by using infant Norway rat pups to study (i) group dynamics, (ii) sex preferences, (iii) group and individual behavior on thermogradients, (iv) group and individual behavior on illumination gradients, and (v) the interaction of thermo- and illumination gradients. Finally, these models will be used to develop Monte Carlo statistical approaches for studying the behavioral development of complex adaptive systems. [unreadable] [unreadable]